Sender Score Certified Fully Qualified Reverse DNS Policy & Deployment Guide
Sender Score Certified policy requires that all certified IP addresses have fully Qualified Reverse DNS (FQ rDNS) established.
As detailed in the Sender Score Certified Email Standards found at (http://www.senderscorecertified.com/about/standards.php) :
"Accountability:
I. (4) The IP address(es) enrolled in Sender Score Certified must have valid reverse DNS entries. The IP address of the host name of the reverse DNS entry must match the IP address of the sending mail server."
The FQ rDNS policy requirement means a sending IP address must have a valid pointer (PTR) record in the Domain Name System (DNS) which resolves to a valid hostname. That hostname must then have an address (A) record in DNS which includes the sending IP address.
Examples
Correct
| SENDING IP | = | PTR VALUE | = | A RECORD VALUE |
| 1.2.3.4 | = | mx.example.net | = | 1.2.3.4 |
Incorrect and Non-Compliant
| SENDING IP | = | PTR VALUE | = | A RECORD VALUE |
| 1.2.3.4 | = | mail.example.net | = | 1.2.6.9 |
| 1.2.3.4 | = | no record, does not resolve | ||
| 1.2.3.4 | = | mail.example.net | = | no record found, does not resolve |
Naming Conventions for Hostnames
It is recommended that rDNS naming not be generic. An example would be for IP address 1.2.3.4 a hostname of 4-3-2-1.company.com. A host name should clearly identify that the machine has been set up as a named host and does not have a common default generic generated naming that simply identifies the telecommunications provider
rDNS should accurately identify the responsible operator of the mail stream(s) transmitted over the IP address. This means that certified IPs should have hostnames ending in certifiedcompanydomain.net, not sometelecommunicationsprovider.net
Examples
Suggested
| 1.2.3.4 | = | mail.certifiedcompany.net | = | 1.2.3.4 |
| 1.2.3.5 | = | mail100.certifiedcompany.net | = | 1.2.3.5 |
| 1.2.3.6 | = | mail101.certifiedcompany.net | = | 1.2.3.6 |
Not Recommended
| 1.2.3.4 | = | nothinghere.someothercompany.net | = | 1.2.3.4 |
| 1.2.3.4 | = | certifiedcompany.net | = | 1.2.3.4 |
| 1.2.3.4 | = | 4-3-2-1.telecommunicationsprovider.net | = | 1.2.3.4 |
Additional Resources
For additional information, please visit the following recommended websites:
http://en.wikipedia.org/wiki/RDNS
http://en.wikipedia.org/wiki/Forward_Confirmed_reverse_DNS
http://en.wikipedia.org/wiki/Hostname
http://en.wikipedia.org/wiki/Dns
http://en.wikipedia.org/wiki/Dns#Types_of_DNS_records
DNS Testing Resources